A position-measuring device of this type is known, for example, from FIG. 6 of JP 2005-326231 A. This position-measuring device is used for sensing the relative position of two objects that are movable relative to one another and is composed of a scanning unit connected to one of the objects and a reflection material measure connected to the other of the two objects. Relative position information regarding the two objects results from interfering superposition of at least two pairs of sub-beams. To this end, a beam incident from a light source is split into at least a first, a second, and a third sub-beam in a first splitting plane by a first splitting element in the scanning unit. The first and third sub-beams are subsequently deflected toward the reflection material measure by deflecting elements in the scanning unit. The second sub-beam is split into at least a fourth and a fifth sub-beam by a second splitting element in the scanning unit, the first and fourth sub-beams propagating toward a first point of incidence, and the third and fifth sub-beams propagating toward a second point of incidence on the reflection material measure. After the first and second pairs of superimposed sub-beams are reflected by the reflection material measure, they propagate toward a first and a second detector, where each of the at least two pairs of sub-beams is brought into interfering superposition. The detectors allow detection of displacement-dependent scanning signals from which, in turn, can be derived position information regarding a vertical and a first lateral direction of displacement of the objects.
Thus, using a position-measuring device of this type, it is possible to simultaneously sense a lateral and a vertical degree of freedom of the two objects that are movable relative to one another.
The device known from JP 2005-326231 A is not suitable for measurement tasks where more than these two degrees of freedom must be sensed using metrological techniques.